Researchers Trace Evolution Of Carbon Molecules Across The Universe

May 15, 2013

Image Caption: Between 2003 and 2005, thanks to its unprecedented sensitivity, NASA’s Spitzer Space Telescope created maps of the tell-tale PAH signature across large regions of space. Credit: NASA JPL

In addition to being a key component of life on Earth, carbon is the sixth most abundant element in the Universe. Yet despite its ubiquitous existence in the cosmos, the evolution of carbon in molecules has been difficult to study. Until now.

Researchers at NASA´s Ames Research Center have taken archival data to chart how chemicals known as complex polycyclic aromatic hydrocarbons (PAHs) vary in different environments. The team examined unusual infrared spectra from NASA´s Spitzer Space Telescope.

“At the time of our discovery that the ‘signature,’ or identifying spectrum, of this unexpected, but common infrared (IR) radiation from space hinted that PAHs might be responsible, we were limited to a handful of small PAHs, very few were available to study,” said Louis Allamandola, a astrophysicist at Ames Research Center.

“To test the idea that PAHs were responsible, we measured and computed PAH spectra under astronomical conditions, creating the world’s largest collection of PAH spectra. Today, our collection contains more than 700 PAH spectra,” he added.

The team found that the PAHs varied significantly in size, structure and electrical charge depending on their environment. To better understand the relationship between the PAH´s properties and their environment, the team studied the Iris Nebula (NGC 7023), a region containing both a hot, volatile environment near the central star as well as a cool outer nebula.

The study revealed larger, more symmetric, electrically charged PAHs nearer to the star, while the cool outer gas cloud was dominated by the smaller, irregularly shaped, neutral PAHs. “The large PAHs take over because they are more robust than the smaller, irregularly-shaped PAHs, which are destroyed by the unshielded star light,” explained Christiaan Boersma, an Ames astrophysicist.

Ultimately, this demonstrates that PAHs are driven by their environment, and it is their very surroundings that can dictate their molecular evolution.

Allamandola notes, “Spitzer detected the PAH signature across the universe and showed PAHs were already forming only a couple of billion years after the Big Bang. Since PAHs are so sensitive to local conditions, analyzing the PAH bands as we did here represents a powerful new astronomical tool to trace the evolution of cosmic carbon and, at the same time, probe conditions across the universe.”